It is often necessary to provide an effective seal between rotatable and stationary parts of a fluid-processing centrifuge. For example, in a blood-processing centrifuge, the centrifuge bowl and associated parts often rotate while conduits making up the fluid inlet and outlet remain stationary. When processing blood, an effective rotary seal is required between these rotatable and stationary elements to insure maintenance of sterile integrity of the blood and to prevent possible contamination of the surroundings when contaminated blood is being processed.
Such a rotary centrifuge seal must be extremely efficient; must minimize leakage of air into or out of the system; must maintain frictional heating at a minimum; must provide good dissipation of heat which may be generated; must be capable of tolerating moderate misalignment and vibration between rotating and stationary parts; and must minimize production of particulate contaminants which might be introduced into the blood being processed. In addition, it is important to have a seal which is low in manufacturing cost thereby making disposability of the entire blood pathway economically feasible after a single use.
A variety of types of rotary centrifuge seals have been developed in an attempt to maximize these qualities. Some examples of rotary centrifuge seals which have proven to be successful are described in U.S. Pat. Nos. 3,409,203 and 3,565,330, issued to Latham. In these patents, rotary seals are disclosed which are formed from a stationary rigid low friction member in contact with a moving rigid member to create a dynamic seal, and an elastomeric member which provices a resilient static seal as well as a modest closing force between the surfaces of the dynamic seal.
Another rotary seal suitable for use in blood-processing centrifuges is described in U.S. Pat. No. 3,801,142 issued to Jones et al. In this seal, a pair of seal elements having confronting annular fluid-tight sealing surfaces of non-corrodable material are provided. These are maintained in a rotatable but fluid-tight relationship by axial compression of a length of elastic tubing forming one of the fluid connections to these seal elements.
Another more recently developed rotary seal has been employed in a blood-processing centrifuge known as the B. T. Bowl which is marketed by Bellco, Mirandola, Italy. In this seal, a ceramic ring member is attached to rotatable elements of the centrifuge and a fixed graphite ring is attached to stationary centrifuge elements. These ring members are in sealing relationship with each other. Additionally, an elastomeric diaphragm is attached at one end to an adapter ring for the graphite ring and at the other end to a stationary part of the centrifuge. While this type of rotary seal helps reduce passage of wear particles into the blood pathway, it lacks adequate provision for assuring that wear particles will be ingested and expelled to the outside without entry into the blood pathway.